Method and apparatus for evaluating a sample through variable angle Raman spectroscopy

Abstract

Described are systems and methods for variable angle Raman spectroscopy, in which electromagnetic radiation will be caused to intersect the sample under investigation at a plurality of angles of incidence, so as to provide Raman scattering spectra at each angle. One example use of measuring such spectra at multiple angles of incidence is to enable evaluation at a plurality of depths within the sample. In many implementations, the range of the angles of incidence will include, and extend to either side, of the critical angle.

I claim: 
     
       1. A method for evaluating a sample, comprising the acts of:
 directing an excitation beam of coherent electromagnetic radiation through a prism to intersect a sample at a plurality of angles of incidence, the plurality of angles including a critical angle of incidence; 
 detecting a Raman scattered spectrum resulting from intersection of the excitation beam with the sample at each of the plurality of angles of incidence; and 
 evaluating at least one property of the sample in reference to at least a portion of the plurality of Raman spectra. 
 
     
     
       2. The method of  claim 1 , wherein the act of directing the excitation beam of coherent electromagnetic radiation comprises emitting the beam from a laser. 
     
     
       3. The method of  claim 2 , wherein the excitation beam of coherent electromagnetic radiation is in the near-infrared range. 
     
     
       4. The method of  claim 1 , wherein the plurality of angles comprises angles at increments of less than 0.02 degrees proximate the critical angle. 
     
     
       5. The method of  claim 1 , wherein the prism has a trapezoidal cross-section. 
     
     
       6. The method of  claim 1 , further comprising the act of recording each Raman scattered spectrum with an imaging device. 
     
     
       7. The method of  claim 1 , wherein the act of evaluating at least one property of the sample comprises comparing at least one detected Raman spectrum with a reference spectrum associated with the property being evaluated. 
     
     
       8. The method of  claim 1 , wherein the act of evaluating at least one property of the sample comprises forming a multi-dimensional representation of the sample through use of a plurality of the detected Raman spectra. 
     
     
       9. A method of evaluating a tissue sample, comprising the acts of:
 directing a beam of a single wavelength of near-infrared electromagnetic radiation through a prism to intersect the tissue sample, wherein the beam is directed to the sample at a plurality of incremental angles of incidence within a first range, the plurality of incremental angles of incidence including a critical angle of incidence, and wherein the prism is configured to communicate Raman scattered electromagnetic spectra to a detector; 
 detecting the Raman scattered electromagnetic spectra through use of the detector; 
 processing the detected electromagnetic spectra to provide a multi-dimensional indication of the molecular composition of the tissue sample at a plurality of depths of investigation. 
 
     
     
       10. The method of  claim 9 , wherein the act of directing a beam of near-infrared electromagnetic radiation at a plurality of incremental angles of incidence comprises
 directing a beam of near-infrared electromagnetic radiation at a first angle of incidence through use of a beam directing mechanism, the first angle of incidence being proximate the critical angle of incidence and to a first side of the critical angle of incidence. 
 
     
     
       11. The method of  claim 10 , wherein the beam directing mechanism comprises a movably mounted source electromagnetic radiation. 
     
     
       12. The method of  claim 10 , wherein the beam directing mechanism comprises a source of electromagnetic radiation and a reflective member between the source of electromagnetic radiation and the prism. 
     
     
       13. A system for evaluating a sample through use of Raman spectroscopy, comprising:
 a source of electromagnetic radiation configured to emit a coherent beam of electromagnetic radiation having essentially a single wavelength; 
 a prism having a sample-engaging surface and a spectra emitting surface; 
 an electromagnetic beam positioning assembly configured to direct the coherent beam of electromagnetic radiation into the prism at a plurality of angles of incidence relative to the sample engaging surface of the prism, the plurality of angles of incidence including a critical angle of incidence; 
 a scattering detector arranged to receive scattered electromagnetic radiation from the spectra emitting surface, and configured to record the received scattered electromagnetic radiation; and 
 a controller assembly configured to control the electromagnetic beam positioning assembly to direct the coherent beam electromagnetic radiation at a plurality of controlled angles of incidence at selected angular increments. 
 
     
     
       14. The system of  claim 13 , wherein the electromagnetic beam positioning assembly comprises a drive mechanism supporting the source of electromagnetic radiation. 
     
     
       15. The system of  claim 13 , wherein the electromagnetic beam positioning assembly comprises:
 a movable mirror positioned to receive the electromagnetic beam and to reflect the beam in the direction of the prism; and 
 a positioning mechanism supporting the movable mirror, and configured to move the mirror through a range of motion to direct the electromagnetic beam. 
 
     
     
       16. The system of  claim 13 , further comprising a reflection detector arranged to receive radiation reflected from the sample through the prism. 
     
     
       17. The system of  claim 16 , wherein the controller assembly is further configured to receive data representative of Raman scattering spectra received from the scattering detector and to correlate the data representative of each Raman scattering spectrum with the incremental position that resulted in the spectrum. 
     
     
       18. The system of  claim 17 , wherein the controller assembly is further configured to receive data representative of reflected electromagnetic radiation from the reflection detector. 
     
     
       19. The system of  claim 13 , wherein the controller assembly comprises:
 one or more processors; and 
 a machine-readable medium storing instructions, which when executed by the one or more processors, results in the following operations,
 orienting the electromagnetic beam positioning assembly to direct the electromagnetic beam at a first angle of incidence relative to the prism sample-engaging surface, 
 activating the laser; 
 receiving data associated with a plurality of spectra of detected electromagnetic scattering from the scattering detector; 
 recording the received data from the scattering detector; 
 orienting the electromagnetic beam positioning assembly to direct the electromagnetic beam at a second angle of incidence, the second angle of incidence being at a determined increment from the first angle of incidence. 
 
 
     
     
       20. The system of  claim 19 , wherein the operations further comprise processing the received data associated with a plurality of spectra of detected electromagnetic scattering to evaluate at least one property of the sample. 
     
     
       21. A system for evaluating a sample through use of Raman spectroscopy, comprising:
 a source of electromagnetic radiation configured to emit a coherent beam of electromagnetic radiation having essentially a single wavelength; 
 a prism having a sample-engaging surface and a spectra emitting surface; 
 an electromagnetic beam positioning assembly configured to direct the coherent beam of electromagnetic radiation into the prism at a plurality of angles of incidence relative to the sample engaging surface of the prism; 
 a scattering detector arranged to receive scattered electromagnetic radiation from the spectra emitting surface, and configured to record the received scattered electromagnetic radiation; 
 a controller assembly configured to control the electromagnetic beam positioning assembly to direct the coherent beam electromagnetic radiation at a plurality of controlled angles of incidence at selected angular increments; and 
 a reflection detector arranged to receive radiation reflected from the sample through the prism; 
 wherein the controller assembly is further configured to receive data representative of Raman scattering spectra received from the scattering detector and to correlate the data representative of each Raman scattering spectrum with the incremental position that resulted in the spectrum; and 
 wherein the controller assembly comprises: 
 one or more processors; and 
 machine-readable storage media storing instructions, which when executed by the one or more processors, results in the following operations, 
 orienting the electromagnetic beam positioning assembly to direct the electromagnetic beam at a first angle of incidence relative to the prism sample-engaging surface, 
 activating the laser; 
 receiving scattering data associated with one or more spectra of detected electromagnetic radiation from the scattering detector; 
 recording the received scattering data from the scattering detector; 
 receiving reflected data associated with electromagnetic radiation from the reflection detector; 
 recording the received reflection data from the reflection detector; and 
 orienting the electromagnetic beam positioning assembly to direct the electromagnetic beam at a second angle of incidence, the second angle of incidence being at a determined increment from the first angle of incidence. 
 
     
     
       22. The system of  claim 21 , wherein the operations further comprise processing the received scattering data associated with a plurality of spectra of detected electromagnetic scattering to evaluate at least one property of the sample. 
     
     
       23. The system of  claim 21 , wherein the operations further comprise processing the received reflection data to evaluate a parameter of the reflection scattering measurement operations.